Synergistic enhancement of electrical conductivity and percolation behavior in epoxy nanocomposites reinforced with hybrid expanded graphite/carbon nanotube/carbon black conductive fillers

Developing electrically conductive polymer composites with high conductivity, low filler loading, and cost-effectiveness is critical for applications including bipolar plates, electromagnetic interference shielding, and conductive coatings. This study systematically investigates the synergistic effects of hybrid carbon fillers on the electrical conductivity and percolation behavior of epoxy-based composites. Expanded graphite (EG), carbon black (CB), and multi-walled carbon nanotubes (CNTs) were incorporated into an epoxy matrix in binary and ternary combinations at various weight percentages using combined mechanical mixing–sonication followed by thermal curing to minimize agglomeration and optimize filler dispersion. Electrical conductivity was determined via four-point probe measurements. The key novelty lies in systematically comparing binary and ternary EG/CB/CNT architectures to identify optimal filler combinations that achieve efficient conductive networks at relatively low total filler content. CNT-containing composites exhibited significantly higher conductivity than CB- or EG-dominated systems due to interconnected conductive pathways and enhanced electron transport. The complementary morphologies of carbon fillers proved synergistic: microscale EG sheets provided extended conductive channels, high-aspect-ratio CNTs bridged conductive regions while reducing inter-filler distances, and CB particles increased local contact density. The optimal ternary composite containing 2.5 wt.% CNT, 2.5 wt.% EG, and 5 wt.% CB achieved the highest electrical conductivity of approximately 123.87 S/cm. These results demonstrate that strategically combining diverse carbon fillers promotes highly interconnected networks and enhances conductivity while reducing individual filler concentrations. The developed hybrid epoxy nanocomposites offer strong potential for advanced applications requiring lightweight, corrosion-resistant, and cost-effective electrically conductive materials.